An international study of salt and blood pressure has been initiated. This study proposes to use population based samples throughout the world to determine the correlation between electrolyte excretion and blood pressure. We propose to obtain four (4) populations in Mississippi to contribute to this study. The four populations are blacks and whites in a rural setting in mid Mississippi, and blacks and whites in Jackson, Mississippi. Each population will be represented by 200 individuals randomly selected from a previously derived roster. Twenty-five are to be in each age/sex/race cell. The age divisions are 20-29, 30-39, 40-49 and 50-59 years of age. Blood pressure will be taken with a "O" muddler apparatus by trained observers, and great care will be taken in urine collection, which will be shipped to a central laboratory for analysis. In addition, we will measure serum uric acid, as a source of information that this may be a marker for abnormality of renal tubular absorption. We will analyze the Jackson data at the completion of the study using uric acid as a co-variate.